Oscillation generator



1,632,054 June 14, 1927. J. T. L. BROWN I OS 0 ILLATI ON GENERATOR Filed Dec. 3; 1923 Mvenfon fa/7n Z2. Eran/n hy my Patented June 14, 19275 UNITED STATES PATENT OFFICE.

JOHN T. L. BROWN, OF NEW BRIGHTON, NEW .YORK, ASSIGNOR T WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

OSCILLATION Application filed December This invention relates to a method of and means'for producing oscillations. and more particularly tothe production of oscillations of variable frequency and amplitude.

It has heretoforebeen proposed to gene]:-

ate oscillations of variable frequency and amplitude 'by continuously rotating a capacity or inductance element included in the frequency determining circuit of an 0scillator, comprising anelectric discharge device having associated input and output circuits coupled in feedback relation.

In a paper published in the journal of A. I. E. E; for May 1920, R. A. Heising points out at page 476 et seq, that the behavior of an oscillator comprising a three electrode electric discharge device having coupled input and output circuits is dependent, among other things, upon the space current, grid current, and oscillating current flowing in the circuits associated with the discharge device.

The present invention provides a self-oscillating system including a three electrode electric discharge device, in which the im pedance of the device is'cyclically controlled to recu rrently produce a succession of electric waves, the frequency and amplitude of which simultaneously vary over a definite range. v

In accordance with this invention an electric discharge device, including a cathode, an anode and a control electrode or grid having its associated input and output'circuits intercoupled to constitute an oscillating sys tern, has a condenser of relatively large capacity, inserted in series with its control electrode, which is gradually charged by current flowing in the grid circuit to render the system non-oscillatory and a'relay in its output circuit to discharge the condenser to restore the system to an oscillatory condi-' tion; whereby the system may be controlled to continuously produce a succession of damped oscillations of desired variable frequency and amplitude. I

The foregoing briefly describes one prac tical embodiment of the invention, but it is not intended to-define the scope of the present invention. The novel features and combinations which are believed to be character:

GENERATOR.

3, 1923. Serial No, 678,117.

istic of this invention will be pointed out with particularity in the sub-joined claims.

One object of the invention is to provide an oscillator adapted to produce a damped oscillation.

Another object is the provision of an arrangement for recurrently producing a train of oscillations, each of which is of variable frequency and amplitude.

Another object of the invention is 'to simplify and improve the operation of oscillation generators for producing oscillations simulating, as to frequencies and energy content, the sound waves of human speech.

F or a complete understanding of the invention reference may be made. to thefollowing specification read with reference to the attached drawing, in which Fig. 1 illustrates the invention as used to supply current of variable frequency and amplitude for agitating the granular particles of a microphone, and I Fig. 2 shows an oscillogramof the oscillating current produced in the anodecathode circuit of the oscillator.

Referring to Fig. 1, there is shown an electric discharge device comprising a vessel l enclosing a cathode 2, an anode 8 and a grid or control electrode 4c.

Heating current is supplied to the cathode 4, and to the cathode of a second discharge device 18 by the source 5.

The input circuit of the discharge device may be traced from the cathode 2 through the tuned circuit, comprising an inductance 7 connected in parallel with a condenser 8, and condenser 9 to the grid 4. In shunt to the condenser 9 is a circuit including a resistance 10 and contacts 11. v

The output circuit maybe traced from the cathode 2, plate source 12, herein shown as a battery, an inductance .13,: coil 14:, relay 15, anode 4e and across thes ace within the device to the cathode 2. condenser 16 connected in shunt to the relay 15 serves as a low impedance path for the oscillating current. Coil 14 is the primary winding of a vent sparking at the relay contacts 11, the

polarizing potential impressed upon the grid of the device will be reduced to Zero or some small value. The system will be restored to anoscillatory condition and at approximately the same instant space current will flow through the relay 15, the armature of which carries one of the contacts 11 will. be pulled up, and the circuit including the resistance 10 will be opened whereby oscillating current will flow through the input circuit and will be rectified by the cooperative action of the cathode and grid to again begin charging the grid and the grid condenser.

The amplitude of the oscillating current flowing in the grid circuit being small and the condenser 9 of relatively large'capacity, an appreciable but small interval is required to accumulate a charge of the desired value in the condenser. the condenser gradually accumulates a charge which makes the grid negative relatively to its cathode.

Because of the gradually charge supplied to the condenser 9, the pee tential impressed upon the grid 4 will con tinuously increase t-rem zero, or some low value, to a relatively high negative value and the impedance of the tubewill. be continually increased and -hence, the effective plate voltage and space current will be gradually decreased until some relatively low value is reached, at which the system ceases to oscillate.

As a consequence otthe reduced space urrent flow, the relay 15, which is very fast acting and sensitive, fails to hold up its armatureand the circuit of the resistance 10 is completed. The grid charge-therefore, is rather abruptly discharged through the relatively low'resistance 10 and the system again-begins to oscillate. This series ofoperations recurs cyclically.

' lVith the arrangement described above, it

will be seen that, duringoscillating periods,

the grid condenser is gradually charged to impose a continuously increasing back'electromotive force to the-flow of the direct current component of the grid current; the grid-cathode and plate-cathode impedances of the discharge device are gradually increased, and hence the efiective impedance to the flow 01 oscillating and space currents During this small interval increasing the tuned circuit to vary and hence change the frequency of the oscillations generated.

It is'pointed out that the shape of the oscillating wave is dependent mainly upon thetrequency range and the rate at which the oscillations are repeated. The frequency in any instance is dependent upon the values of the inductance,-capacity and effective resistance of the coils and condensers in the oscillating system, all of which are relatively const'ant,-and the impedances of the coupled grid and plate circuits which are va-,

ria-ble, since they are dependent upon the changing grid voltage. The rate at which the-oscillations are repeated depends upon, among other things, the value of the capacity charged by the oscillating currentv flowing in the grid circuit and the quickness of response of the relay 15.

The constancy of operation of the oscillater is largely dependent upon the operation of the relay in the plate circuit. This relay should be very fast acting and sensitive and its operation can be considerably improved by providing it with an armature which does notchatter. a The coil 14- is inductively associated with a coil 17 included in the input circuit of a discharge device 18, which is shunted by a high resistance, to control its operation, whereby the amplified variable oscillating current generated by the oscillator is supplied through a repeating coil 19 to a load circuit.

As apractical use to which an oscillator of this type may be applied, it is herein shown as an element of an arrangement for testing telephone transmitters.

-material of the microphone is continuously agitated in a manner similar to that pro duced by speech waves.

The oscillator used in the microphone testing arrangement, includes an electric esaoae 3 discharge-device having an external impedance of the order of 2000 ohms,- when no polarizing potential is impressed upon its Y grid,-and an amplifying factor of'about 3.

Space current is supplied to the device at 110 volts, the input and output circuits are connected by a repeating coil, each winding of which has an impedance of one henry at 900' cycles, an ohmic resistance of-about 42 ohms and the coefficient of coupling between the windings of the repeating coil is approximately 1. The condenser included in the input circuit has a capacity oftwo microfarads. The relay included in the plate circuit has a resistance of 1000 ohms, is adapted to operate at three milliamperes and to release at 2.6 milliamperes.

Under these conditions the initial oscillating current flowing in the input circuit is twelve milliamperes and the final input current is zero. The initial space current, average measured with a D. C. meter, is thirty milliamperes, and the final space current is .4 milliampere. The relay operates in approximately one two-hundrcdths of a second .and is adapted to complete the leak path when the space current falls to .4 milliampere. The damped wave is repeated about twenty-five times per second.

Fig. 2 illustrates an oscillogram of the oscillating current generated by the system described above. The frequency of the oscillating current at the point A on this curve is about 700 cycles and .at the point B the frequency is about 1900 cycles. The amplitude as shown by this curve varies simultaneously and inversely with the frequency. Assuming that at the point A the amplitude is represented by unity, the amplitude of the wave at the mid-point C will be represented by one-half, and its amplitude at the point B by one-tenth.

The frequency range of the oscillating current produced by the oscillator described above, corresponds to the most important lporti'on, of the range used in commercial telephony and the use of-an oscillating cur- "rent of variable frequency and amplitude which is interrupted, as supplied by this os cillator, serves to maintain the granular material of a telephone transmitter in an agitated condition which is similar to that resulting from speech waves.

By using a discharge device having the proper characteristics associated with input and output circuits having resistances, inductances and capacities of. the proper values an arrangement adapted to produce variable oscillating current above or below the audible frequency range may be provided.

While in the preceding description certain circuits, specific details and a practical example have been above described for the purpose of completelyand clearly disclos- .circuits, details or use given, but onlyby the scope of the attached claims.

-What is claimed is:

'1. In a self-oscillating system including an electric discharge device having a leak path, the method of producing oscillations of va'-- riable frequency and amplitude which comprises alternately changing the conductivity of the leak path from a high to a low value, for varying the electrical conditions of the system.

2. The method of operating a threeelectrode space discharge device which comprises causing the device to generateoscillations at a frequency within the audible range, and cyclically at a frequency adjacent the lower limit of the audible range causing said device to react upon itself to stop and recommenceoscillating.

3. A self-oscillating system comprising a 'three-ele trode electric dischargeidevice having coupled input and output circuits, means for gradually varying the impedance of the space path of said, device and abruptly restoring said space path to itsoriginal impedance.

4. A self-oscillating system comprising a three-electrode electric discharge device, and means for periodically causing the potential -impressed upon one of the electrodes of said device to be varied and abruptly restored to its initial value whereby oscillations of variable frequency and amplitude are produced.

5. A self-oscillating system comprising an electric discharge device comprising a cathode, an anode, a control electrode and input and output circuits therefor coupled in feed back relation, means for impressing a gradually increasing potential upon said control electrode and for then abruptly discharging the impressed potential.

6. A self-oscillating system comprising an electric discharge device comprising a cathode, an anode, a control electrode and input and output circuits therefor coupled in feedback relation, means under the control of the generated oscillations to accumulate a gradually increasing potential upon said control electrode and for abruptly-discharging the 8. A self-oscillating system comprising an 7 electric discharge device having a cathode,

an anode, a control electrode and .input and output circuits therefor coupled in feed-back relation, means included in said input circuit for accumulating a gradually increasing negative potential charge and impressing said charge upon said control. electrode, and means included in said output circuit for es-v tablishinga conductive path about said negative charge accumulating means.

9. A self-oscillating system comprising an electric discharge device having a cathode, an anode,'a control electrode and coupled input and'output circuits thereforr'a condenser included in the input circuit, as elay in the output circuit, a circuit in shunt of said condenser adapted to be controlled by said relay said condenser and said relay cooperating whereby a gradually increasing negative potential charge is impressed upon said control electrode and then discharged.

10. A generator of oscillations comprising a space discharge device provided With asso-- ciated circuits and Jarelay included in one of said circuits, means for controlling said device 'to gradually reduce the current supplied to said relay until the latter operates to close another of said circuits, whereby said generator produces oscillations of continuously varying frequency.

11. A generator of oscillations comprising a space discharge device provided with external circuit connections and a relay, said circuit connections being provided with means including said relay for varying the impedance-of a part of said circuit connections over a Wide range, whereby said generator produces oscillations of continuously varying frequency. v

12. A generating system for producing oscillations of frequency range and relative intensity of components adapted to simulate the energy distribution of the waves of audible speech which comprises a three-element space discharge device having coupled circuits associated therewith, and means included in said circuits for controlling said system to produce a succession of'damped trains of waves, the components of each train increasing in frequency as their amplitudes decrease.

In witness whereof, I hereunto subscribe my name this 27th day of November, A. D.

, JOHN T. L. BROYVN. 

